Composite set



Feb. 19, 1929. 1,702,309 H. NYQUIST COMPOSITE SET Filed Dec. 18, 1926.Balawwing/Wtwork 5 INVENTOR. lzn ma A TTORNEYS.

Patented Feb. 19, 1929.

UNITED STATES PATENT OFFICE.

HARRY NYQUIST, OF MILLBURN, NEVT JERSEY, ASSIGNOR TO AMERICAN TELEPHOIJEAND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

COMPOSITE SET.

Application filed December 18, 1928.

known as a composite set whereby the incoming telegraph and telephonecurrents may be separated and diverted to their respective circuitswithout interference with each other. The composite set, furthermore,functions to prevent the outgoing telegraph currents from entering thetelephone path at the terminal facilities and vice versa. Heretofore,composite sets have separated the telephone and telegraph channels bymeans of frequency selectivity. The improved composite set of thisinvention not only makes use of frequency discrimination or selectivityto separate the incoming telephone and telegraph channels, but embodiescertain novel features and principles with respect to the prevention ofinterference between the different types of currents originating in thedifferent telephone and telegraph branches at the terminal facilities.By satisfying certain impedance relations in the composite set of thisinvention,

it is possible to obtain a conjugate relationship between the telephoneand telegraph branch so that interfering currents from either of thesecannot enter the other regardness of frequency discrimination.Furthermore, by making the impedance of both the telegraph and telephoneterminal apparatus substantially equal to a common pure resistance, theimpedance of the two, as seen through the composite set, to the line,also is substantially equal to a pure resistance at all frequencies,Also the impedance of the line to the telephone and telegraph, as seenthrough the composite set, may be made pure resistance, line impedance,or other desired impedance. This will tend to improve the transmissioncharacteristics of the systems by obviating echoes, reflections, andreflection losses. Further features or objects of the invention willappear more fully from the detailed description hereinafter given.

Serial No. 155,728.

The invention may be more fully understood from the followingdescription, together wlth the accompanying drawing in the F igures 1 to8 of which the invention is illus trated. Figs. 1, 2, 4 and 5 illustrateschematically, certain principles involved in the invention. In Figs. 3and 6, the invention is shown inschematic form. Fig. 7 shows a practicalembodiment of the invention, and Fig. 8 a modification thereof.

One of the principles utilized in the com posite set of this inventionis illustrated in Fig. l, in which the telegraph and telephone branchesare shown tentatively as connected to the opposite sides of a Wheatstonebridge composed of the equal resistances 7",, 1' 7' and 1",. Accordingto the well known prin ciples of the Wheatstone bridge current bommg inover the telegraph branch will not be transmitted out over the telephonebranch as the points P and P are of equal potential. Likewise, currentfrom the telephone branch will not be transmitted out over the telegraphbranch as the latter would be connected to the equi-potential points Pand P In other words, a conjugate relationship is established betweenthe telephone and telegraph branch so that interfering currents fromeither of these branches cannot enter the other, even without frequencydiscrimination. The line circuit is shown schematically as as sociatedwith one of the arms of the bridge.

In Fig. 2, a capacity C is substituted for the resistance arm 1, of Fig.1 and the resistance arm 1*, is changed into an inductance L. By properadjustments of the constants of the arms of the Nheatstonebridge, aconjugate relationship may still be established between the telegraphand telephone branches so that interfering currents from either of thesecannot enter the other regardless of frequency discrimination. Becauseof the capacity C, the low frequency currents coming in from thetelegraph branch will not take the path C73, but will take the path 03L.On the other hand, the high frequency currents from the telephonebranch, due to the inductance L, will not take the path In", but willfollow the path 13C. Accordingly, by utilizing an inductance and acapacity as arms of the VVheatstone bridge and connecting the telephoneand telegraph branches thereto, as shown, we find that currents fromboth branches will be transmitted through the cal arm 1 Accordingly, theline circuit will be associated with this arm 1, in the manner to bepointed out hereinafter.

The composite set of the invention is shown in schematic form in thearrangements 0t Fig. 3. The arrangement and proportionment of theelements of Fig. 3 will be more apparent from a discussion of Figs. land 5.

In Fig. lis shown an arrangement oi i111 pedances which has thefollowing properties:

( 1) Opposite resistances are conjugate.

(2) The impedance connected to any one oi. the tour resistances is apure resii-itance equal. to B. These facts are made more obvious it' thefigure is redrawn to an equivalent form, as shown in Fig. 5, in whichthe same impedauccs are shown in the term of a balanced lVhcatstonebridge, which is reaiflily tami liar and is known to have the twoproperties above stated. This figure also permits us to state byinspection what the necessary relations must be in order that thenetwork, as shown in Fig. l, should have these properties. The equationexpresses the necessary and suflicient condition.

Accordingly, if we now substitute the telc phone and telegraph terminalcircuits and apparatus for the right and left resistance elements R ofFig. 4: and connect the line circuit in place of the lower resistanceand make the upper resistance a balancing; network, it will be apparentthat we will have the composite set shown schei'natically in Fig. 3 andthis composite set will have the above referred to properties.Accordingly, by thus satisfying certain impedance relations and byconnecting the telegraph and telephone branches, as shown, a conjugaterelationship is established between these branches so that interferingcurrents from either of these branches cannot enter the other regardlessof frequency discrimination. It is point ed out that energy from themember marked Linc circuit in Fig. 3 is not equally divided between thetelephone and telegraph branches but that the ratio of division is atuinctimi. of frequency. At a frequency determined by the relation tweenthe line and network or in other words, conjugacy between the telephoneand telegraph branches.

It is pointed out that it is also desirable to make the impedance ofboth the telegraph and telephone terminal apparatus substanti ally equalto a common pure resistance. Under such conditions, the impedance of thetwo as seen through the composite from the line equals a pure resistanceat all he quencics. This will tend to obviate echoes, reflections andreflection loss and. materially improve transmission. it may bepreferable, however, to make the impedance facing the telephone ortelegraph branches, or both, an inqiedancc easy to simulate by means ofsimple network,-perhaps pure resistance 01' line in'ipedance. It may,therefore, be desirable to make the 7 and r members of the bridgeimpedance diti'erent from pure inductance and capacity, remoectively,and r, member different tron: pure resistance or line impedance. This,obviously, may be done it the condition tor conjugacy is maintained suchas r ap 1t Frequency discrimination will be obtained if r, be animpedance high at telegraph frequencies and low at telephone frequenciesand r, the reverse.

In carrying the design from the schematic l orm shown in Fin. 3 to aform, which practically applicable, certain facts have to be considered.in the first place, the line met with in practice is balanced to ground.In the second place, it is not permissible to establish this balance bymeans of a transt'ornr er liiecauw-r it is necessary to transm t directcurrent. dome "areinust also be taken so that the number of connectionsbetween the composite set and the circuits which it connects should notbe greater than necessary.

In Fig. 6 is shown an arrangement which applies one balancing networkllN to each of the two line wires. This gives two sets of places for thetelephone and telegraph to be connected. The telegraph case can bereduced to a single one immediately by making the connection indicatedin the dotted line. The two telephone branches can be combined in asimilar manner by the use of a transformer. The correspondingarrangement is shown in F 1 which is arranged in a more usual manner andincludes connections for a phantom circuit.

The arran 'emcnt shown in Fig. 7 is not as good or desiraliile in repect to toe matter of deriving the phantom circuit, shown as theconnection Ph. because the phantom telenot derive the benefit of balancedisc initiation. The arrangeshown in Fig". i5 is more at actory in phonecircuit (i( the not in that the plat-atom circuit is put on ruc lmsie-r:rhe de circuits. The

apparat showi'! above the dotted line in iii and is external to thecomposite set proper, but should be grouped with the apparatus below thedotted line for the sake of simplifying the wiring. The apparatus abovethe dotted line is made up of three transformers which have beendesignated I, II and III. I and II are the side circuit transformers andIII is the phantom circuit transformer. The poling of the variouswindings is indicated by the numerals which are so arranged that currentflowing from an odd to an even terminal produces magnetism of a givensign. The cross-fire among the various telegraph circuits seems to betaken care of, particularly if the neutral point is grounded, asindicated by the dotted connection in Fig. 8.

While the invention has been disclosed as embodied in certain specificarrangements which are deemed desirable, it is understood that it iscapable of embodiment in many other and widely varied forms withoutdeparting from the spirit of the invention as defined by the appendedclaims.

What is claimed is:

1. A V'Jheatstone bridge substantially balanced for all frequencieshaving one set of opposite arms comprising a line circuit and abalancing network and another set of opposite arms comprising aninductance and a capacity, respectively, a telegraph circuit connectedto the junction point of said line circuit and said capacity and to thejunction point of said inductance and said balancing network, and atelephone circuit connected to the junction point of said line circuitand said inductance and the junction point of said balancing network andsaid capacity.

2. A line circuit, a balancing network, an inductance, a capacity, theimpedances of said elements being so adjusted and said elements being soarranged as to form a Wheatstone bridge substantially balanced for allfrequencies, and a telephone circuit and a tele graph circuit soassociated with said elements as to be in conjugate relationship witheach other. I

3. A /Vheatstone bridge substantially balanced at all frequencies havingone set of opposite arms comprising a line circuit and a balancingnetwork and another set of opposite arms comprising an inductance and acapa ,ity, and signaling circuits of different types connected to theopposite junction points of the arms of said bridge.

4. A transmission line and a composite set associated therewith, saidcomposite set comprising a telephone circuit and a telegraph circuit soarranged as to be in conjugate relatio-nshlp to each other and havingthe constants of said circuits so adjusted that the impedances presentedto said circuits will each be substantially equal to a common pureresistance.

5. A balanced VVheatstone bridge having one set of opposite armscomprising a line circuit and a balancing network and another set ofopposite arms comprising an inductance and a capacity, a telegraphcircuit connected to the junction point of said line circuit and saidcapacity and to the unction point of said inductance and said balancingnetwork, and a telephone circuit connected to thejunction point of saidline circuit and said inductance and the junction point of saidbalancing net work and said capacity, the constants of said telephoneand telegraph circuits being so adjusted that the impedances of saidcircuits will each be substantially equal to a common pure resistance.

6. A. balanced Nheatstone bridge having one set of opposite armscomprising a line circuit and a balancing network and another set ofopposite arms, one of which comprises an impedance much larger fortelephone than for telegraph currents, and the other of which comprisesan impedance much larger for telegraph than for telephone currents, atelegraph circuit connected to the junction point of said line circuitand the last mentioned one of said second set of opposite arms, and tothe junction point of said network and the first mentioned one of saidsecond set of opposite arms, and a telephone circuit connected to thejunction point of said line circuit and the first mentioned one of saidsecond set of opposite arms and to the junction point of said networkand the second mentioned one of said second set of opposite arms.

7. A balanced Wheatstone bridge having one set of opposite armscomprising a line circuit and a balancing network and another set ofopposite arms one of which comprises an impedance much larger fortelephone than for telegraph currents and the other of which comprisesan impedance much larger for telegraph than for telephone currents, atelegraph circuit connected to the junction point of said line circuitand the last mentioned one of said second set oi opposite arms and tothe junction point of said network and the first mentioned one of saidsecond set of opposite arms, and a telephone circuit connected to thejunction, point of said line circuit and the first mentioned one of saidsecond set of opposite arms and to the junction point of said networkand the second mentioned one of said second set of opposite arms, theconstants ofthe arms of said bridge being so adjusted that as seen fromeither said telephone circuit or said telegraph circuit the impedance ofthe bridgewill be substantially a pure resistance within a workingfrequency range.

8. A balanced VVheatstone bridge having one set of opposite armscomprising a line circuit and a balancing network and another set ofopposite arms one of which comprises an impedance much larger fortelephone than for telegraph currents and the other of which comprisesan impedance much larger for telegraph than for telephone currents, atelegraph circuit connected to the junction point of said line circuitand the last mentioned one of said second set of opposite arms and tothe junction point of said network and the first mentioned one of saidsecond set of opposite arms, and a telephone circuit connected to thejunction, point of said line circuit and the first mentioned one of saidsecond set of op posite arms and to the junction point of said networkand the second mentioned one of said second set of opposite arms, theconstants of the arms of said bridge being so adjusted that as seen fromeither of said telephone circuit or said telegraph circuit the impedanceof the bridge will be substantially equal to the line impedance withinthe Work ing frequency range.

In testimony whereof, I have signed my name to this specification, this17th day of December, 1926.

HARRY NYQU 1ST.

